1. Field of the Invention
The present invention relates to an image forming apparatus which forms a test image on a recording medium and measures the density of the test image, and then determines an image forming condition based on the measurement result.
2. Description of Related Art
A method for adjusting image processing characteristics in image forming apparatuses, such as a copying machine or a printer, includes: starting the image forming apparatus; after warming-up operation, forming a specific pattern image on an image holding member (e.g. a photosensitive drum) measuring the density of the pattern image; and based on a density value, changing an operation parameter of a circuit such as a .gamma. corrector for determining an image forming condition, to maintain image quality.
In a case where image forming characteristic is changed due to change in environmental conditions, again the specific pattern image is formed on the image holding member. Also, the density of the formed pattern image is measured again, and the measurement results is fed back to the circuit for determining the image forming condition such as the .gamma. corrector. Thus, image quality can be maintained in accordance with the amount of the change in the environmental conditions.
However, if the image forming apparatus is used for a long term, the measurement result of test pattern density on the image holding member might not correspond with that of an actually-formed image on a paper. For example, a cleaning blade for cleaning excessive toner is provided in contact with the photosensitive drum. The contact state for a long time may roughen the photosensitive drum surface, and relation between the amount of toner adhered onto the photosensitive drum and reflected light amount from the photosensitive drum upon density measurement may change. Accordingly, in an image forming apparatus used for a long term, if the image forming condition is determined using a density conversion parameter based on density data from initial measurement, image of corresponding density to the image data cannot be obtained.